This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for a multi-symbol matched filter estimation of a symbol in a received signal having a predictable inter-symbol interference.
Modulators often have to utilize premodulation filters to reduce splatter and to meet regulatory guidelines. Such filters, when used with modulators for data symbols can smear the symbol boundaries, causing inter-symbol interference, which can, in turn, reduce receiver sensitivity.
In many applications, receiver sensitivity is of the utmost importance. An example is the inbound (portable-to-base station) channel of a two-way messaging system, where the relatively weak transmitter of the portable unit requires a robust base receiver having great sensitivity in order to achieve a sufficient balance between the inbound and outbound links.
Thus, what is needed is a method and apparatus that can achieve a high receiver sensitivity even in the presence of substantial inter-symbol interference introduced by a relatively severe premodulation filter.
An aspect of the present invention is a method for a multi-symbol matched filter (MSMF) estimation of an evaluation symbol in a received signal having a predictable inter-symbol interference. The method comprises the steps of selecting a portion of the received signal comprising the evaluation symbol, along with at least one preceding symbol received immediately before the evaluation symbol, and at least one following symbol received immediately after the evaluation symbol; and prefixing to the portion of the received signal at least one previously estimated symbol received immediately before the portion, thereby producing an evaluation portion. The method further comprises the steps of comparing the evaluation portion with a plurality of templates equal in length to the evaluation portion and comprising different combinations of trial symbols and the at least one previously estimated symbol, prefixed to the trial symbols; and estimating the evaluation symbol to be equal to a trial symbol in one of the plurality of templates having a highest correlation with the evaluation portion, the trial symbol having a position matching that of the evaluation symbol in the evaluation portion.
Another aspect of the present invention is a multi-symbol matched filter (MSMF) detector for estimating an evaluation symbol in a received signal having a predictable inter-symbol interference. The detector comprises a processing system for processing the received signal. The processing system includes a processor, and a memory coupled to the processor for storing operating variables and software for programming the processing system. The processing system is programmed to select a portion of the received signal comprising the evaluation symbol, along with at least one preceding symbol received immediately before the evaluation symbol, and at least one following symbol received immediately after the evaluation symbol; and to prefix to the portion of the received signal at least one previously estimated symbol received immediately before the portion, thereby producing an evaluation portion. The processing system is further programmed to compare the evaluation portion with a plurality of templates equal in length to the evaluation portion and comprising different combinations of trial symbols and the at least one previously estimated symbol, prefixed to the trial symbols; and to estimate the evaluation symbol to be equal to a trial symbol in one of the plurality of templates having a highest correlation with the evaluation portion, the trial symbol having a position matching that of the evaluation symbol in the evaluation portion.
Another aspect of the present invention is a receiver for receiving a signal having a predictable inter-symbol interference. The receiver comprises a receiver element for receiving and down-converting the signal, and a multi-symbol matched filter (MSMF) detector coupled to the receiver element for estimating an evaluation symbol in the signal. The detector comprises a processing system for processing the received signal. The processing system includes a processor, and a memory coupled to the processor for storing operating variables and software for programming the processing system. The processing system is programmed to select a portion of the received signal comprising the evaluation symbol, along with at least one preceding symbol received immediately before the evaluation symbol, and at least one following symbol received immediately after the evaluation symbol; and to prefix to the portion of the received signal at least one previously estimated symbol received immediately before the portion, thereby producing an evaluation portion. The processing system is further programmed to compare the evaluation portion with a plurality of templates equal in length to the evaluation portion and comprising different combinations of trial symbols and the at least one previously estimated symbol, prefixed to the trial symbols; and to estimate the evaluation symbol to be equal to a trial symbol in one of the plurality of templates having a highest correlation with the evaluation portion, the trial symbol having a position matching that of the evaluation symbol in the evaluation portion.